How long do you normally test an update for Zend Framework before pushing it out into a productions project. We can break this question up into minor updates 1.6.0 -> 1.6.1 or maybe a major update 1.6.2 -> 1.7.0. Obviously you don't release it if it add bugs to your code.
Also, as with most other server software updates normally people have a window of time they like to wait and watch the community before even attempting an update on a development environment. How long do you even wait to start the process?